(Related note: Your cropped avatar is one of the few reasons I'm bummed about the new avatar size.)
EDIT: And on topic, nobody over 6 feet weighing under 180 has big arms. Focus on gaining muscular bodyweight and building total body strength in the 6-12 rep range. That means squats, deads, rows, presses, curls, and extentions, among other things.
What does your current weekly training look like? And how much bodyweight have you gained in the last three months?